The invention concerns the production of an individualized orthodontic brace for treating a patient intended to be used mainly in the case of a lingual technique, i.e. with the brace disposed on the non-visible posterior face of the teeth.
Such braces conventionally include:                at least one orthodontic wire, in other words a metal wire exerting on the teeth a force tending to move them from their initial unsatisfactory position, called the “wrong position”, to a final satisfactory position, called the “corrected position”; and        a series of brackets each provided with at least one groove for receiving an orthodontic wire; these brackets are individually fixed to the teeth of the patient in a particular position enabling the orthodontic wire to transfer to the teeth the rotation forces necessary to move them from the wrong position to the corrected position during the treatment.        
Usually one or more orthodontic wires are used, with a single series of brackets each including one or more grooves.
Lingual orthodontic techniques, which have the esthetic advantage that the brace is practically invisible from the outside, began to be developed around 1970. However, at the time they relied on entirely manual design and fabrication of the braces and their use was highly complex. This is because an important element in the success of the treatment is the correct positioning of the bracket and its groove on the tooth, especially relative to its rotation center. This is because this position determines the orientation of the forces that are imposed on the corresponding tooth and thus the orientations of the tooth in various directions in space when it is in the final corrected position. This positioning is much more difficult to achieve with the lingual technique than with the labial or vestibular technique in which the brace is disposed on the anterior face of the teeth, because of the marked angulation of the posterior faces of the teeth. This angulation is farther away from the center of rotation of the tooth relative to the bracket than in the case of a labial technique. This means that a slight error in the positioning of the bracket may position the groove incorrectly, thus rendering the brace incapable of providing the required correction of the position of the tooth.
It is therefore particularly important to position the brackets very accurately, especially on the incisors and canines, the shapes of the internal faces of which are more complex and variable than those of the premolars and molars.
This positioning is usually effected by devices commonly referred to by orthodontists as jigs, an example of which is described in the document US-A-2009/0136890. That jig consists of a plastic material block provided on its lower or upper face with a housing the configuration of which is such that the end of a given tooth can be inserted in it. This insertion is possible in an accurate and effective manner for the success of the treatment only if the morphology of each tooth has been individually digitized beforehand from an imprint of the dental arch of the patient and that morphology has been fed digitally into the control software of a block fabrication machine. Thus the block is produced with a cavity in which the end of the tooth can be inserted exactly. The block also includes a hook-shaped support member having three consecutive sections at right angles to each other. A first section passes through the block, sliding in an appropriate orifice. A third section has its end shaped to be inserted into the groove of a bracket so as to hold it when fitting the bracket and to be easily disengaged therefrom once the bracket has been fitted. The second section joins the other two. To fit the bracket, it is placed at the end of the support member, the tooth is capped with the block and traction is exerted on the support member to press the sole of the bracket against the base previously coated with an orthodontic adhesive. When the adhesive has been polymerized, the support member is disengaged from the bracket and the block is removed.
This device has a number of drawbacks, however. The blocks and support members are bulky, which makes them difficult to fit and uncomfortable for the patient. Moreover, the accuracy of the positioning of the brackets is not always sufficient. On the one hand, the block encompasses only the upper part of the tooth, because it cannot cover a large portion of the posterior face in order not to impede the fitting of the bracket. It follows that there may be a relatively large play in positioning the block during the operation. On the other hand, the multi-part structure of the device means that inaccuracies in the design and fabrication of the various components are cumulative.